[Aboot] Support boot from device

[mate4st]

Why I did it

I have a Arista Switch which has a slot for an m2 ssd drive that is by default not used. I added the m2 SSD. However the boot script and some other tooling, assumes that everything is installed on the internal flash and not the drive (SSD). The boot-config file is never updated on the flash, which leads to a failing boot as aboot always reads the boot-config from flash.

How I did it

Ensure boot-config is mirrored to the flash when updated.

How to verify it

Install SONiC on Arista device with an additional m2 SSD, referenced as drive.

Description for the changelog

Add support for drive device for aboot

[mate4st]

Support for the installer: https://github.com/sonic-net/sonic-utilities/pull/2469